Conventional lagoon based wastewater treatment systems rely generally on open air lagoons to permit aerobic and anaerobic treatment of wastewater. A lagoon is any earthen basin for containing a body of water, such as a treatment reactor cell. Lagoons and other wastewater treatment ponds or basins are typically constructed by excavating land to create a reservoir area. If desired, berms can then be built around the perimeter of the reservoir area to extend the walls of the reservoir above ground level. Quite often, a lagoon is lined with a layer of clay to serve as a barrier. For example, environmental regulations typically require a subgrade clay layer of uniform thickness, for example 5 feet thick and having uniform water content. Often times a plastic liner made of high-density polyethylene may be placed over the entire interior surface defined by the reservoir and the berm area. The liner is made of sheet strips of high density polyethylene (HDPE) which overlap in an abutting fashion and are then welded or cemented together to create a water impermeable and erosion control line.
Once the lagoon is constructed and lined the wastewater liquid or sludge material is then pumped into the lagoon on top of the liner and/or the clay which is lining the lagoon. This liner facilitates not only maintaining the wastewater in the reservoir or lagoon but also in maintaining any turbulent water flow in the surface from eroding the berm and banking of the lagoon. The lagoon or pond is subject to water fluid level changes as well as a turbulence of the surface in particular from aeration of the wastewater which can erode the banking and the berm. The liner is instrumental in protecting the underlying clay and soil lining forming the lagoon particularly where the turbulent water contacts the berm and banking.
Lagoon based water treatment systems require a large amount of space, on the order of several acres and often necessitate the large interior encompassing liner in conjunction with the lagoon construction to facilitate containment of the wastewater and to prevent erosion of the banking around the lagoon. This is tremendously expensive where an entire lagoon system must be covered with a liner, not only upon initial construction but upon replacement or fixing of a compromised liner.
Such traditional lagoon-based liner systems have several shortcomings. Because of the large size of the liners where the liners cover the entire interior of the lagoon, the liners which are generally impermeable material must be constructed on-site usually in large strips, where the strips are heat sealed together along their edges after being placed in an empty lagoon. This of course means that the lagoon must be emptied and cannot be used for the time period in which the new liner material is placed inside. It is tremendously labor intensive, time-consuming and expensive to assemble such liners and empty the lagoons if a liner needs to be fixed or replaced.
Additionally, multiple floating “tanks” are required to treat screened sewage within the lagoon. Waste water must be pumped into and out of each lined containment structure before and after treatment, respectively. For this operation, each tank for example may have a static volume of approximately 1,437,500 gallons and be able to turnover 437,500 gallons with pumps adding and removing the waste at a peak flow of approximately 5600 gallons per minute (gpm). A reduction in costs in maintaining the liners and containment structures is needed with minimal maintenance requirements and delays in operation.